PhD Defense Christopher Williams "Direct and Large-Eddy Simulation of Turbulent Hypersonic Boundary Layers In Thermochemical Non-Equilibrium"

Activated by elevated temperatures in the shock layers of hypersonic vehicles, non-equilibrium thermochemical effects including dissociation/recombination phenomena and ionization, together with near-wall turbulence structures, mediate the unsteady heat fluxes, ablation rates, and vibrational loading imposed during high-speed flight. By leveraging computational-methods development for non-equilibrium flows, high-resolution direct numerical simulations of hypersonic boundary layers are performed to characterize turbulence-chemistry interaction over non-catalytic and ablative surfaces at re-entry conditions. With the introduction of graphite ablation, a Crocco-Busemann-like relation between streamwise velocity and ablation-product molar fractions emerges in the mean, while further spectral analysis reveals the significance of near-wall streaks in mediating oxidation-driven differential ablation. Dynamic subgrid-scale closure models for species and internal-energy fluxes are formulated and evaluated a posteriori with high-enthalpy wall-modeled large-eddy simulations. Combined with a finite-rate chemistry wall model, the dynamic formulation is shown to accurately predict aerothermal loading in turbulent reacting hypersonic boundary layers, at a computational cost more than two orders of magnitude lower than direct simulation.